Colorectal cancer (CRC) is the third most common form of cancer, resulting in over half a million deaths each year. Despite the use of chemotherapies and biologics, the five-year CRC survival rate is only a little over 50%. Immunotherapy is an exciting new line of attack that is particularly well suited for the treatment of CRC. Immunotherapeutics are expected to be efficacious in treating genetically heterogeneous tumors and drug- resistant tumors, which make up a significant portion of CRC tumors. In CRC patients, Th17 immune cells induce a tolerant and angiogenic tumor environment correlating with poor prognosis, while Th1 and CTL/CD8 cells are associated with a tumor killing environment and correlate with survival. Interleukin-2 inducible T cell kinase (ITK), is a member of the Tec kinase family downstream of the T cell receptor and is involved in Th17 cell, but not Th1 cell survival and activation. Therefore, selectively blocking ITK will inhibit Th17 cells while sparing Th1 and CTL/CD8 cells. While Ibrutinib (a pan-Tec kinase inhibitor blocking BTK, ITK and TXK) has shown promise in the clinic, our approach specifically targets ITK, thereby removing the negative effects of inhibiting TXK (decreased Th1 response) and BTK (increased infection risk and bleeding). In this SBIR Phase 1 application, we propose to develop the first ITK inhibitor drug candidate for the treatment of CRC. We have developed an innovative kinase drug discovery platform (KINect) that exploits our proprietary kinase inhibitor library in the context of structure-based drug design (SBDD) to rapidly identify and develop active, drug-like chemical cores into drug candidates. Using this approach and our own ITK crystal structure we utilized our extensive drug development experience to identify a set of potent, selective, covalent and proprietary lead ITK inhibitor compounds that block Th17 cell activation. We propose to further develop ITK drug candidates to test the central hypothesis that selective inhibitors of ITK will be efficacious immunotherapeutics for the treatment of CRC by inhibiting immunosuppressive Th17 cells, while sparing Th1 and CD8/CTL cells, thereby facilitating the anti- tumor amplification alone or in combination with checkpoint inhibitors. The proposed research focuses on the following specific aims: (1) Optimize the TXK selectivity and T cell activity of ITK inhibitor drug candidates as immunotherapeutics to treat CRC and (2) Determine ITK inhibitor efficacy in murine in vivo models of Th17 function and CRC. SBIR Phase 2 studies will focus on generating additional preclinical in vivo CRC efficacy data as well as pharmaceutical, pharmacokinetic and safety data, advancing the program to IND and initiation of human Phase 1 clinical evaluation in CRC patients. Supporting studies will include genetically engineered mouse CRC models, regulatory toxicology, pharmacokinetics and drug product synthesis. We anticipate a co- development partnership license following Phase 1/2 clinical studies with a deal value of >$200M. Given the need for new CRC therapies, the development of an effective ITK inhibitor drug will address a key unmet need and have a major medical impact.